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A DNA test reveals that Hannes Streif, 40, has a father who is not his biological father.
Photo: Yves Bachmann
Thanks to a DNA test he found online, lawyer Hannes Streif discovered that he was conceived through anonymous sperm donation. That’s how he found 14 half-siblings—and the number keeps growing.
Discovering his roots, perhaps finding out if he had inherited his father’s Crohn’s disease—those were Streif’s expectations when the Zurich lawyer ordered a DNA test online.
“I never doubted for a second that my social reality was also my biological one,” says Streif. But when the results arrived in his mailbox a month later, they shattered his previous worldview in an instant.
The results suddenly revealed a half-brother in Austria. “My first thought was: They mixed up my sample,” recalls the 44-year-old. But when the brother told him over the phone that his parents had been in Bern for treatment in the late 1970s, Streif began to suspect something.
In passing, Hannes Streif confronted his mother. Her answer was brief: “Your father is not your biological father.” For Streif, it felt as if one of the two pillars on which he had built his life had simply crumbled away.
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What shapes our health long before our first breath? Why do we underestimate our risks? What truly strengthens us? And how do we find greater clarity in an overstimulated world? The seventh edition of the Sanitas Health Forecast—which also features a profile of attorney Hannes Streif—is titled “Prepared for the Future” and addresses the big questions of our time: origin and upbringing, illness and risks, strength and regeneration, as well as mental health and resilience. The Sanitas Health Forecast 2026 is a publication by Wörterseh Verlag and will be available in bookstores starting June 16, 2026, or can be ordered online.
“You look in the mirror and feel like a stranger to yourself,” says Streif. “There was someone inside me who had always been there, who makes up half of me, and I didn’t know it.”
The roots of this lifelong lie lie in an era of social constraints. Due to treatment with cortisone, Streif’s social father became infertile. But at the time, having a child was part of the ideal image of the middle-class family.
So the parents decided on anonymous sperm donation. The doctors also supported the secrecy.
The sperm donation was sold to the parents with the promise that no one would ever find out anyway.
The fact that sperm from different donors was mixed into a “cocktail” back then made the search for biological truth nearly impossible—or so it seemed.
But Hannes Streif is a lawyer. “Being lied to is part of the job,” he says. “I took on the challenge.” Over four years of meticulous, painstaking work, he reconstructed a family tree of 1,600 people using genetic “pooling” and by combing through church records.
He discovered that his biological father had donated his sperm once or twice a week for years. “Even if you factor in the miscarriage rate, he might have fathered 300 children. That’s a small army.”
But he could no longer confront his biological father with this; he had already passed away.
What remains is a scar. Despite the pain, Streif does not regret the search. Once a year, he meets with his newly found half-siblings.
There are 14 so far, but the search continues passively. Whenever someone with a similar genome takes an online DNA test, Streif gains a new sibling.
For Hannes Streif, transparency is the most important thing today. His appeal to other parents is clear: “Tell your children if they were conceived through sperm donation. It will come out sooner or later.”
The search is over, the mystery solved. “It was as if I had found my second arm again,” he says. He can finally go on living a normal life again—with the certainty of who he really is.
